CPR time indicator for a defibrillator data management system

ABSTRACT

A system is disclosed wherein patient data, such as an electrocardiogram (“ECG”) signal or a chest impedance measurement signal, collected by a defibrillator device during a resuscitation event is analyzed and processed by a computing device to provide an assessment of CPR administered during the event. The CPR assessment results in one or more CPR figures of merit that relate to temporal characteristics of the CPR relative to the duration of the event. In one embodiment, the CPR figure of merit represents a percentage of the event period during which chest compressions were administered to the patient.

TECHNICAL FIELD

The present invention relates generally to defibrillator systems. Moreparticularly, the present invention relates to a data management systemfor a defibrillator system.

BACKGROUND

A normal human heart pumping pattern is called a sinus rhythm, and thepattern is regulated by the body's biological pacemaker within the upperright chamber of the heart, which is commonly referred to as the rightatrium. This natural pacemaker, which is generally referred to as thesinoatrial (“SA”) node, sends electrical signals to the right and leftventricular muscles in the lower chambers of the heart. The ventricularmuscles then implement the pumping action under the control of the SAnode. The right ventricular muscle pumps blood to the lungs foroxygenation, and the left ventricular muscle pumps the oxygenated bloodto various parts of the body.

In certain circumstances, the normal or sinus heartbeat rhythm may beadversely affected as a result of some type of malfunction in theheart's electrical control system. When this type of malfunction occurs,an irregular heartbeat may result, causing the ventricular muscles topump ineffectively, thus reducing the amount of blood pumped to thebody. This irregular heartbeat is generally referred to as anarrhythmia.

A particularly serious arrhythmia is known as ventricular fibrillation(“VF”), which is a malfunction characterized by rapid, uncoordinatedcardiac movements replacing the normal contractions of the ventricularmuscles. In this event, the ventricular muscles are not able to pumpblood out of the heart, and there is no initiation of a heartbeat. VFrarely terminates spontaneously, and is therefore a leading cause ofsudden cardiac arrest. The unpredictability of VF and other irregularheart beat conditions exacerbates the problem, and emphasizes the needfor early therapeutic intervention to prevent the loss of life.

Defibrillators are devices for providing life-saving electrical therapyto persons experiencing an irregular heat beat, such as VF. Adefibrillator provides an electrical stimulus to the heart in an attemptto convert the irregular heat beat to a normal sinus rhythm. Onecommonly used type of defibrillator is the external defibrillator, whichsends electrical pulses to the patient's heart through externalelectrodes applied to the patient's chest. External defibrillators maybe manually operated (as are typically used in hospitals by medicalpersonnel), semi-automatic, semi-automated, fully automatic, or fullyautomated devices, where they can be used in any location where anunanticipated need may occur.

In practice, defibrillation pulses are administered to the patient whennecessary, and cardio-pulmonary resuscitation (“CPR”) is administeredbetween pulses. CPR includes the delivery of chest compressions to thepatient (to stimulate blood flow) and the delivery of ventilations tothe patient (to provide air to the lungs). Recent statistical studiessuggest that the amount of time devoted to CPR during a typicalresuscitation event may be less than optimal in real world situations.Although some of the defibrillator usage time is necessarily occupied byrhythm analysis and defibrillation functions—which in most casespreclude the simultaneous delivery of CPR—there may be an undesirableamount of “wasted” time during which neither the defibrillator devicenor the caregiver are actively administering treatment to the patient.

Presently, there are no straightforward and elegant ways to assess theproportion of time that chest compressions and/or ventilations wereperformed during a resuscitation event. Such assessments can be usefulduring post-event review of a defibrillator usage case. Currently,caregivers or case reviewers must make educated guesses via laboriousevaluation of ECG signal artifacts (which can be highly variable fromcase to case), captured scene audio (which may not be available for alldefibrillator devices), device prompts, and expectations of caregiverbehavior.

Accordingly, it is desirable to have a system for providing quantitativepost-event feedback related to the amount and proportion of time thatchest compressions and/or ventilations were performed during a cardiacarrest response treated by a defibrillator device. In addition, it isdesirable to have a system for providing other figures of merit relatedto the delivery of CPR during a resuscitation event, where such figuresof merit are determined from post-event patient data analysis.Furthermore, other desirable features and characteristics of the presentinvention will become apparent from the subsequent detailed descriptionand the appended claims, taken in conjunction with the accompanyingdrawings and the foregoing technical field and background.

BRIEF SUMMARY

A system and method for assessing CPR performed during a resuscitationevent processes patient data collected during the event for analysis ina post-event manner. The patient data, which can be an ECG signal and/ora patient impedance signal, is analyzed to determine temporal indicatorsrelated to a CPR figure of merit. The system is configured to generate asuitable report containing the CPR figure of merit for review andassessment of the treatment administered to the patient.

The above and other aspects of the invention may be carried out in oneform by a method for assessing CPR performed during resuscitationtherapy. The method involves obtaining an event time interval for aresuscitation event and processing post-event data for a patient todetermine a temporal CPR percentage representing a percentage of theevent time interval during which chest compressions were administered tothe patient. The post-event data represents at least one patient signalelectronically captured during the resuscitation event, such as an ECGsignal or a patient impedance signal captured by a defibrillator device.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be derived byreferring to the detailed description and claims when considered inconjunction with the following figures, wherein like reference numbersrefer to similar elements throughout the figures.

FIG. 1 is an illustration of an external defibrillator system connectedto a patient;

FIG. 2 is a schematic representation of an external defibrillator systemconfigured in accordance with the invention;

FIG. 3 is a schematic representation of a computing device configured inaccordance with the invention;

FIG. 4 is a flow diagram of a CPR assessment process according to theinvention; and

FIGS. 5 and 6 are example graphs of patient data signals captured by adefibrillator device during a resuscitation event.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary or the following detailed description.

The invention may be described herein in terms of functional and/orlogical block components and various processing steps. It should beappreciated that such block components may be realized by any number ofhardware, software, and/or firmware components configured to perform thespecified functions. For example, an embodiment of the invention mayemploy various integrated circuit components, e.g., memory elements,digital signal processing elements, logic elements, look-up tables, orthe like, which may carry out a variety of functions under the controlof one or more microprocessors or other control devices. In addition,those skilled in the art will appreciate that the present invention maybe practiced in conjunction with any number of practical defibrillatorsystems and that the system described herein is merely one exemplaryapplication for the invention.

For the sake of brevity, conventional techniques related to ECGmonitoring, patient impedance measurement, defibrillator device control,digital signal processing, data transmission, and other functionalaspects of the systems (and the individual operating components of thesystems) may not be described in detail herein. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent example functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical embodiment.

FIG. 1 depicts a defibrillator system 20 that is configured to deliverdefibrillation therapy to a patient 22, such as a victim of VF. Thedefibrillator system 20 includes, but is not limited to, an externaldefibrillator device 24 having a connection port 26 that is configuredto receive one or more cables or wires corresponding to one or morepatient electrodes 32/34. In practice, external defibrillator device 24can be any number of external defibrillators, such as an automaticexternal defibrillator or an automated external defibrillator, asemi-automatic or semi-automated external defibrillator, or a manuallyoperated external defibrillator. Fully- or semi-automated or automaticdefibrillators are sometimes referred to as “AEDs.”

External defibrillator device 24 preferably includes a user interface 27having a display 28 that is configured to visually present variousmeasured or calculated parameters of patient 22 and/or other informationto the operator (not shown) of external defibrillator device 24. Forexample, display 28 can be configured to visually present thetransthoracic impedance, ECG, and/or other physiology signals of patient22. User interface 27 can also include one or more input devices (e.g.,switches or buttons) 30 that are configured to receive commands orinformation from the operator. External defibrillator device 24 isconfigured to generate a charge that is delivered to patient 22 as thedefibrillation therapy pulse via electrodes 32/34.

Electrodes 32/34 are typically multifunction electrodes in that they areconfigured both to provide defibrillation therapy and to sense one ormore physiology and/or physical parameters of patient 22 that arereceived by external defibrillator device 24 at connection port 26. Thisis a typical configuration in an AED type device; it will be understoodby those skilled in the art that electrodes may be designed differentlyfor different machines. Other defibrillators, including for examplemanual defibrillators, may also have an additional set of electrodes(not shown), in addition to the multifunction electrodes, used toreceive ECG information. These additional electrodes, ECG electrodes,are generally smaller than therapeutic/multifunction electrodes, and ECGelectrodes typically plug into a separate port (not shown) than thetherapeutic/multifunction electrodes. As is understood in the art, ECGelectrodes typically have a three wire lead, though other arrangementsare possible. The signals provided by the one or more electrodes 32/34are preferably evaluated by external defibrillator device 24 todetermine, among other things, whether a defibrillation shock should beapplied to patient 22 in accordance with techniques known to those ofordinary skill in the art. This external defibrillator device 24 can, insome embodiments, also evaluate the signals provided by the one or moreelectrodes 32/34 to determine the waveform parameters of thedefibrillation shock (e.g., sinusoidal, monophasic, biphasic, truncated)as well as magnitude and duration; AEDs often include a preprogrammedenergy protocol. As is understood in the art, manual defibrillators mayallow for a manual selection of shock parameters.

FIG. 2 is a schematic representation of a defibrillator 100 suitable foruse with the invention as further described herein. Although not shownin FIG. 2, defibrillator 100 may include a number of functionalelements, logical elements, and/or hardware components that supportconventional defibrillator features unrelated to the invention.Defibrillator 100 generally includes a processor 102, a suitable amountof memory 104, a data communication element 106, a monitoring circuit108, and a defibrillation therapy circuit 110. Defibrillator 100 mayinclude a data bus 112 to facilitate communication of data or controlsignals between some or all of the above components.

Processor 102 may be any general purpose microprocessor, controller, ormicrocontroller that is suitably configured to control the operation ofdefibrillator 100. Memory 104 may be realized as any processor-readablemedium, including an electronic circuit, a semiconductor memory device,a ROM, a flash memory, an erasable ROM, a floppy diskette, a CD-ROM, anoptical disk, a hard disk, an organic memory element, or the like. Asdescribed in more detail below, memory 104 is capable of storing patientdata captured during a resuscitation event, e.g., ECG signals 114,patient impedance signals 116, or the like.

Communication element 106 is configured to communicate with a remotecomputing device (described below). In particular, communication element106 is suitably configured to communicate post-event patient data to theremote computing device in accordance with at least one datacommunication protocol. As used herein, “post-event patient data” and“post-event data” refers to data that is transferred, analyzed,reported, or otherwise processed after a resuscitation event (except inthe case of real-time handling of patient data as described in moredetail below). Thus, although defibrillator 100 obtains patient dataduring the resuscitation event, post-event patient data can be stored bydefibrillator 100 for post-event transfer, analysis, and processing. Forexample, post-event data may include a patient impedance signal, apatient ECG signal, and/or data recorded, collected, or generated bydefibrillator 100 during an event, including, without limitation,defibrillation pulse delivery times, voice prompt times, and rhythmanalysis times.

In the example embodiment, communication element 106 communicates withthe remote computing device in accordance with at least one standardizeddata communication protocol (either wireless or wired). Suchstandardized data communication protocols include, without limitation:Bluetooth; IEEE 802.11 (any variation thereof); Ethernet; IEEE 1394(Firewire); GPRS; USB; IEEE 802.15.4 (ZigBee); or IrDA (infrared).Communication element 106 may be realized with hardware, software,and/or firmware using known techniques and technologies. For example,defibrillator device 100 may include a wireless port configured tosupport wireless data communication with the remote computing deviceand/or a cable or wire port configured to support data communication,via a tangible link, with the remote computing device. In this regard,communication element 106 and any corresponding logical or softwareelements, individually or in combination, are example means forproviding the post-event patient data to the remote computing device.

Alternatively (or additionally), the post-event data may be transferredto the remote computing device using portable storage media. Forexample, the post-event data can be transferred or copied from memory104 onto a portable storage device for transport to the remote computingdevice. The portable storage media may include, without limitation, amagnetic disk, a semiconductor memory device, a flash memory device, afloppy diskette, an optical disk (e.g., a CD or a DVD), a hard disk, orthe like.

Alternatively (or additionally), the post-event data may be transferred,via communication element 106 or using portable storage media asdescribed above, from defibrillator 100 to another medical device suchas a second defibrillator. For example, where a first responder (forexample, a police officer, firefighter or bystander) has used an AED totreat a patient, it is desirable to transfer data stored on the AEDconcerning that rescue event (including patient physiological data andinformation on therapies applied to the patient) to a defibrillator orother medical device used by medical personnel (for example, emergencymedical technicians) who take over care of the patient. This transferreddata may later be subsequently transferred from the medical device tostill another medical device or to a computing device. The post-eventdata from defibrillator 100 may be merged with other data from themedical device for transfer to yet another medical device or computingdevice.

In operation, defibrillator 100 communicates with patient sensors thatmay be applied to or attached to the patient undergoing treatment. In apractical embodiment, patient sensors may be realized as conventionaldefibrillation therapy electrode patches 118 that are capable ofmonitoring patient data and delivering defibrillation pulses to thepatient. For example, electrode patches 118 are preferably configured todetect the patient's ECG signal and the patient's chest impedance usingtechniques known to those skilled in the art (chest impedance istypically measured by applying a high frequency variable level carrierwave into the patient via electrode patches 118). In a practicalembodiment, defibrillator 100 can concurrently sample the ECG and chestimpedance signals during a resuscitation event. Although only twopatient sensors are depicted in FIG. 2, a practical embodiment mayemploy any number of patient sensors defining any number of ECG leads,any number of patient sensors defining any number of chest impedancemeasurement circuits, and any number of patient sensors configured tomonitor, sense, or detect other patient related data or signals that maybe utilized to assess the quality of CPR as further described herein.For example, patient sensors may include one or more pressure sensors,one or more accelerometers, or any number of sensors, transducers, ordetectors that indicate characteristics of CPR such as, for example,rate of compression delivery, duty cycle of compression delivery, depthof compressions, or force of compression delivery.

Therapy circuit 110 is generally responsible for the application ofdefibrillation pulses to the patient. In an automated or automaticdefibrillator, therapy circuit 110 may determine whether adefibrillation pulse is warranted and, if so, charge and discharge thedefibrillation pulse circuit as needed. Therapy circuit 110 preferablyoperates in accordance with known techniques and methodologies and,therefore, will not be described in detail herein.

Monitoring circuit 108 is suitably configured to receive the patientdata or signals from patient sensors 118. As described above, such datamay represent the patient ECG signal and/or the patient chest impedancesignal. Monitoring circuit 108 may process the received data into aformat for storage in memory 104, into a format for interpretation orfurther analysis by defibrillator 100 (therapy circuit 110 inparticular), into a format compliant with a data communication protocolto facilitate transfer to a remote computing device, and/or into anysuitable format. In practice, monitoring circuit 108 may perform analogto digital conversion on the received signals or otherwise condition thereceived signals for subsequent handling by defibrillator 100. In onepreferred embodiment that handles post-event data, monitoring circuit108 facilitates storage of data representing the patient ECG signal 114and storage of data representing the patient chest impedance signal 116.In this context, the stored post-event data represents at least onepatient signal electronically captured during the resuscitation event.The storage of such post-event data enables subsequent review andanalysis of the resuscitation event.

FIG. 3 is a schematic representation of a computing device 200configured in accordance with the invention. Computing device 200 may beany known device or system configured to support the CPR assessmenttechniques described herein, including, without limitation: a standarddesktop personal computer, a portable computer such as a laptop computeror a tablet computer, a personal digital assistant (“PDA”), a suitablyconfigured mobile telephone, or the like. Computing device 200 generallyincludes a processor 202, an appropriate amount of memory 204, a datacommunication element 206, logic corresponding to a CPR merit algorithm208, a report generator 210, a display element 212, and a user interface214.

As with most commercially available general purpose computing devices, apractical computing device 200 may be configured to run on any suitableoperating system such as Unix, Linux, the Apple Macintosh OS, anyvariant of Microsoft Windows, a commercially available real timeoperating system, or a customized operating system, and it may employany number of processors 202, e.g., the Pentium family of processors byIntel, the processor devices commercially available from Advanced MicroDevices, IBM, Sun Microsystems, or Motorola, or other commerciallyavailable embedded microprocessors or microcontrollers.

The logical and functional elements of computing device 200 maycommunicate with system memory (e.g., a suitable amount of random accessmemory), and an appropriate amount of storage or “permanent” memory. Forcomputing device 200, memory 204 may represent such random access memoryand/or such permanent memory. The permanent memory may include one ormore hard disks, floppy disks, CD-ROM, DVD-ROM, magnetic tape, removablemedia, solid state memory devices, or combinations thereof. Inaccordance with known techniques, operating system and applicationprograms reside in the permanent memory and portions thereof may beloaded into the system memory during operation. In accordance with thepractices of persons skilled in the art of computer programming, theinvention is described herein with reference to symbolic representationsof operations that may be performed by the various computing componentsor devices. Such operations are sometimes referred to as beingcomputer-executed, computerized, software-implemented, orcomputer-implemented. It will be appreciated that operations that aresymbolically represented include the manipulation by the variousmicroprocessor devices of electrical signals representing data bits atmemory locations in the system memory, as well as other processing ofsignals. The memory locations where data bits are maintained arephysical locations that have particular electrical, magnetic, optical,or organic properties corresponding to the data bits.

When implemented in software or firmware, various elements of thesystems described herein (which may reside at defibrillator 100 orcomputing device 200) are essentially the code segments or instructionsthat perform the various tasks. The program or code segments can bestored in a processor-readable medium or transmitted by a computer datasignal embodied in a carrier wave over a transmission medium orcommunication path. The “processor-readable medium” or “machine-readablemedium” may include any medium that can store or transfer information.Examples of the processor-readable medium include an electronic circuit,a semiconductor memory device, a ROM, a flash memory, an erasable ROM(EROM), a floppy diskette, a CD-ROM, an optical disk, a hard disk, afiber optic medium, a radio frequency (RF) link, or the like. Thecomputer data signal may include any signal that can propagate over atransmission medium such as electronic network channels, optical fibers,air, electromagnetic paths, or RF links. The code segments may bedownloaded via computer networks such as the Internet, an intranet, aLAN, or the like.

The specific configuration, operating characteristics, and functionalityof display element 212 and user interface 214 can vary depending uponthe practical implementation of computing device 200. For example, ifcomputing device 200 is a desktop computer, then display element 212 maybe a CRT, LCD, or plasma monitor, and user interface 214 may include akeyboard and a pointing device such as a mouse or touchpad (userinterface 214 may also include a speaker system, a microphone system, acamera system, or the like). Alternatively, if computing device 200 is aPDA, then display element 212 may be a small scale LCD integrated intothe PDA itself, and user interface 214 may include a small scale keypad,a stylus writing screen, a touchpad, or the like.

Computing device 200 may be configured to support data communicationwith defibrillator 100. Such data communication may be carried out overany number of wireless data communication links and/or any number ofwired data communication links. Alternatively, computing device 200 mayobtain post-event data from defibrillator 100 via a portable storagedevice. To facilitate such data communication, computing device mayinclude data communication element 206. In particular, communicationelement 206 may be suitably configured to receive post-event patientdata (captured by defibrillator 100) in accordance with at least onedata communication protocol as described above in connection with datacommunication element 106. Furthermore, communication element 206 andcomputing device 200 may be configured for compatibility with aparticular data file format used by the defibrillator. For example,communication element 206 and computing device 200 may be configured tosupport different patient data file formats that may be used bydifferent manufacturers of defibrillator devices. Communication element206 may be realized with hardware, software, and/or firmware using knowntechniques and technologies. Communication element 206 and anycorresponding logical or software elements, individually or incombination, are example means for receiving post-event patient datafrom a remote defibrillator device such as defibrillator 100.

Computing device 200 is configured to assess the CPR administered duringa resuscitation event after completion of the event. In this regard,computing device 200 may include a logical, program, or processingelement corresponding to CPR merit algorithm 208. In a practicalembodiment, CPR merit algorithm 208 may be realized as a softwareprogram maintained in memory 204 and performed by processor 202. Forexample, CPR merit algorithm 208 and one or more associated applicationprograms may be embodied in a medical informatics software system suchas the CODE-STAT™ product from Medtronic, Inc. Briefly, CPR meritalgorithm 208 analyzes the post-event patient data (e.g., the patientECG signal and/or the patient chest impedance signal obtained fromdefibrillator 100) and generates one or more figures of merit thatdescribe the CPR administered during the resuscitation event. Althoughthe following description focuses on figures of merit related to theapplication of chest compressions, the invention also contemplatesfigures of merit related to the application of ventilations. The figuresof merit may be alphanumeric values, graphs, charts, scores, or thelike. In a practical embodiment, report generator 210 formats andgenerates one or more reports for review by a user of computing device200. The report may be displayed on display element 212, printed,rendered in a format suitable for facsimile or email transmission,rendered in an audible format, or otherwise generated for communicationto the user. In practice, a report may include, without limitation:patient identification data; event or incident identification data; agraphical representation that summarizes the distribution of variousactivities during the resuscitation event (such as CPR, application ofdefibrillation therapy pulses, or the like); interval statistics (suchas a ratio or percentage of time devoted to chest compressions and/orventilations, an average rate of compressions/ventilations, an effectiverate of compressions/ventilations, and the average duty cycle ofcompressions/ventilations); and overall statistics (such as the totalduration of defibrillator device use, the total duration of CPR, thetotal duration of compressions/ventilations, the number of analysesperformed, the number of pulse checks performed, the number ofdefibrillation pulses applied, the number and duration of “hands-off”pauses, and the like).

FIG. 4 is a flow diagram of a CPR assessment process 300 according tothe invention. Process 300 may be performed by a computing system, suchas computing device 200, following a resuscitation event. Process 300assumes that patient data has been captured (and possibly stored) by adefibrillator, such as defibrillator 100. The various tasks performed inconnection with process 300 may be performed by software, hardware,firmware, or any combination thereof. For illustrative purposes, thefollowing description of process 300 may refer to elements mentionedabove in connection with FIGS. 1-3. In practical embodiments, portionsof process 300 may be performed by different elements of the remotecomputing system. It should be appreciated that process 300 may includeany number of additional or alternative tasks, the tasks shown in FIG. 4need not be performed in the illustrated order, and process 300 may beincorporated into a more comprehensive procedure or process havingadditional functionality not described in detail herein.

CPR assessment process 300 begins by downloading post-event patient datato the computing device (task 302). Alternatively, process 300 may beginby transferring post-event patient data from portable storage media tothe computing device. During task 302, the computing device receives thepost-event data from a remote defibrillator device. The post-event datarepresents at least one patient signal that was electronically capturedduring a resuscitation event. For example, the post-event data mayrepresent the patient ECG signal and/or the patient chest impedancesignal captured during a given resuscitation event. Post-event data mayalso include device events or actions (for example, rhythm analyses,voice prompts, or defibrillation pulses) that are marked or annotated bythe device at the appropriate location in the ECG and/or impedancesignals. In the preferred embodiment, the computing device processes atleast the chest impedance signal captured by the defibrillator. Task 302(or its equivalent) may be performed at any time after the resuscitationevent has ended.

FIG. 5 is a graphical representation of an example patient ECG signal402 and an example patient chest impedance signal 404 corresponding to aresuscitation segment during which the patient experiences VF, adefibrillation therapy pulse is administered to the patient, and thenCPR is administered to the patient. The lower graph in FIG. 5 representsa continuation of the upper graph in FIG. 5. These example signals areprovided to aid in the description of CPR assessment process 300 and arenot intended to limit the scope of the invention in any way. Thegraphical representation depicted in FIG. 5 may be generated by adefibrillator device for display at the device, at an evaluationcomputer system, and/or for storage as post-event data. In FIG. 5, thedisplayed text items are annotations generated by the defibrillatordevice at specific times during the resuscitation event. Thus, forexample, the instant of the defibrillation pulse is indicated by thetext “Shock 1, 200 J,” and a downward pointing arrow above that text atthe instant that the ECG signal stops (defibrillation pulse deliverycauses the ECG display to go blank for a few seconds). Similarly, thepost-therapy rhythm analysis time and outcome is automatically annotatedby the defibrillator device (indicated by the text “Segment 1,” “Segment2,” and “Nonshockable”), as is a subsequent voice prompt to begin CPR(indicated by the text “CPR Prompt”). The large spikes in the patientchest impedance signal 404 that begin immediately preceding the “CPRPrompt” annotation represent chest compressions. In this regard, asystem according to one example embodiment of the invention identifieseach of the compression spikes, and then calculates all of the variousmeasures and metrics described herein. For example, the time point ofthe defibrillation pulse and the time point of the first compression ofthat sequence can be used to derive a “post-defibrillation pause” figureof merit.

FIG. 6 is a graphical representation of an example patient ECG signal406 and an example patient chest impedance signal 408 corresponding to aresuscitation segment during which chest compressions interspersed withventilations are administered to the patient. The lower graph in FIG. 6represents a continuation of the upper graph in FIG. 6. These examplesignals are provided to aid in the description of CPR assessment process300 and are not intended to limit the scope of the invention in any way.The graphical representation depicted in FIG. 6 may be generated by adefibrillator device for display at the device, at an evaluationcomputer system, and/or for storage as post-event data. A normal ECGsignal conveys a regular wave of heartbeats, however, during VF, the ECGsignal is erratic or flat. The chest impedance signal is usuallycharacterized by relatively broader peaks and valleys that indicateventilations and relatively narrower peaks and valleys that indicatechest compressions. In FIG. 6, the narrow pulses of patient chestimpedance signal 408 represent compressions, while the two broaderpulses (identified by reference number 410) represent ventilations.Typical chest compression rates during CPR would range from 60 to 120compressions per minute, with recommended rates of 80 to 100compressions per minute. Typical ventilation rates would range from 6 to35 per minute, with recommended rates nearer the lower end of thatrange. A typical resuscitation event will include an interval of CPRdelivered in sequences of 15 compressions interspersed by twoventilations, followed by an interval of analysis of the ECG todetermine whether delivery of a defibrillating pulse is advisable, andthen possibly by one or more defibrillation pulses, if the analysisrecommends defibrillation. A five-to-one ratio may also be part of CPRteaching; that is, some settings and providers will pause every fivecompressions to deliver one breath. The process of CPR, followed by ECGanalysis, followed by defibrillation therapy, may be repeated in wholeor in part during the resuscitation event. A system according to anexample embodiment of the invention may identify the compression spikesand/or the ventilation spikes for purposes of calculating one or morefigures of merit for the resuscitation event.

Referring again to FIG. 4, CPR assessment process 300 also obtains anevent time interval for the resuscitation event (task 304). The eventtime interval may be any period of time spanning any portion of theresuscitation event. In one preferred embodiment, task 304 obtains thetotal duration of the resuscitation event, which may be represented bythe time period defined by the start and end of the patient ECG signal.Alternatively, the total time may be defined as the time period fromwhen the patient is first detected by the defibrillator to the time whenthe defibrillator is turned off (or when the patient sensors are removedfrom the patient). In practice, the event time interval obtained duringtask 304 can be derived from the post-event data, or it may be aparameter generated by the defibrillator for use by the computingdevice. For example, the computing device may be configured to analyzethe post-event data to determine the duration of the event. It should beappreciated that CPR merit algorithm 208, processor 202, and anycorresponding logical or software elements, individually or incombination, are example means for obtaining the event time interval.

Depending upon the format of the post-event data received from thedefibrillator, it may be necessary for the computing device to extractor otherwise resolve the patient ECG signal from the post-event data(task 306) and extract or otherwise resolve the patient chest impedancesignal from the post-event data (task 308). These tasks may be performedto facilitate efficient analysis and interpretation of the respectivepatient signals by CPR merit algorithm 208 as explained below.

Generally, CPR assessment process 300 processes and analyzes certaincharacteristics of the post-event data (e.g., the ECG signal and/or thepatient impedance signal) to identify qualities and features of the CPRchest compressions or CPR ventilations administered to the patientduring the resuscitation event (task 310). The manner in which thepost-event data is examined may vary depending upon the desired figureof merit or the specific type of post-event data under consideration.For example, in one embodiment, the post-event data is analyzed toidentify periods during which chest compressions were administered tothe patient (task 312). As shown in FIG. 5, chest compressions aretypically administered in multiples during a given CPR cycle. Forexample, a CPR protocol may call for 100 chest compressions during a 60second cycle. Task 312 may identify the start time of each cycle, theend time of each cycle, the number of chest compressions actuallydelivered during the cycle, the rate of chest compression deliveryduring the cycle, the length of pauses between chest compressions withina cycle, the duration of each chest compression, the duty cycle of thechest compressions, or the like. In a practical embodiment, task 312 mayidentify periods during which ventilations were administered to thepatient. In this regard, task 312 may identify the number ofventilations administered to the patient, the rate at which ventilationswere administered to the patient, the duration of each ventilation, orthe like. In accordance with one practical embodiment, task 312 may beperformed by CPR merit algorithm 208 by analyzing fluctuations in thepatient ECG signal, fluctuations in the patient chest impedance signal,and/or other temporal artifacts in the post-event data to identify,characterize, or quantify the chest compressions and/or ventilationsadministered during the event. In this regard, CPR merit algorithm 208,processor 202, and any corresponding logical or software elements,individually or in combination, are example means forprocessing/analyzing the post-event data.

CPR assessment process 300 may also analyze characteristics of thepost-event data, such as event markers or annotations automaticallygenerated by the defibrillator device and inserted into the post-eventdata, to identify times during the resuscitation event when thedefibrillator device took certain actions, such as analyzing thepatient's heart rhythm, administering defibrillation pulses to thepatient, or providing voice prompts to the rescuer (task 314). Followingtask 314, the computing device can statistically recreate theresuscitation event, including the timing of chest compressions andventilations, as well as the timing of rhythm analyses, defibrillationpulses, and voice prompts. Generally, CPR assessment process 300 derivesat least one CPR figure of merit from the post-event data, where the CPRfigure of merit is indicative of temporal characteristics of chestcompressions administered to the patient and/or temporal characteristicsof ventilations administered to the patient, relative to the timing ofsome aspect of the resuscitation event. Example CPR figures of merit aredescribed in detail below.

One example CPR figure of merit relates to the amount of time between afinal chest compression of a CPR cycle and the application of the nextdefibrillation pulse. As used herein, this figure of merit refers to apre-defibrillation pause indicator that represents the period between adefibrillation pulse and a final chest compression administered to thepatient prior to that defibrillation pulse. In this regard, CPRassessment process 300 may determine one or more pre-defibrillationpause indicators for the given resuscitation event (task 316). Inpractice, CPR merit algorithm 208 can determine this period byidentifying the last compression in a cycle, marking the time of thatcompression, identifying the next defibrillation pulse, and marking thetime of that pulse. In some cases, a lengthy pause between chestcompressions and a defibrillation pulse is undesirable and, therefore, apre-defibrillation pause indicator of such a lengthy pause willadversely affect the CPR figure of merit.

Another example CPR figure of merit relates to the amount of timebetween a defibrillation pulse and the next chest compression. As usedherein, this figure of merit refers to a post-defibrillation pauseindicator that represents the period between a defibrillation pulse andan initial chest compression administered to the patient subsequent tothat defibrillation pulse. In this regard, process 300 may determine oneor more post-defibrillation pause indicators for the given resuscitationevent (task 318). In practice, CPR merit algorithm 208 can determinethis period by identifying a defibrillation pulse, marking the time ofthat pulse, identifying the next chest compression, and marking the timeof that compression. As mentioned above, in some cases, a lengthy pausebetween a defibrillation pulse and the next chest compression isundesirable. In such cases, a post-defibrillation pause indicator of alengthy pause will adversely affect the CPR figure of merit.

Another example CPR figure of merit relates to the frequency of chestcompressions administered during a given compression cycle. As usedherein, this figure of merit refers to a compression frequency indicatorthat represents a period between individual chest compressions in agiven cycle. To this end, CPR assessment process 300 may determine oneor more compression frequency indicators for the given event (task 320).In a practical embodiment, CPR merit algorithm 208 can determine thisfrequency by identifying a CPR compression cycle, counting the number ofchest compressions administered during that cycle, and marking the timeof each compression. Thereafter, CPR merit algorithm 208 can generate anapproximate compression frequency (in compressions per unit of time)corresponding to the given CPR cycle. Depending upon the specific CPRprotocol, the compression frequency indicator will adversely affect theCPR figure of merit if it significantly departs from the idealcompression frequency called for by that CPR protocol.

Yet another example CPR figure of merit relates to the timing of CPRcompression cycles administered during a given resuscitation event. Asused herein, this figure of merit refers to a CPR cycle indicator thatrepresents a period between adjacent CPR compression cycles. Thus, CPRassessment process 300 may determine one or more CPR cycle indicatorsfor the given event (task 322). In a practical embodiment, CPR meritalgorithm 208 can determine this indicator by identifying the CPRcompression cycles, marking the start time and end time for each cycle,and calculating the time period between any two adjacent cycles. In somecases, a lengthy pause between chest compression cycles is undesirable.In such cases, a CPR cycle indicator of a lengthy pause will adverselyaffect the CPR figure of merit. An alternative way of looking at thiswould be to use the identified timing of compressions to calculate therate, and then to compare the calculated rate to desired compressionrates, which nominally would be 80-100 compressions per minute. Ratesabove or below the desired rates should be discouraged (and the figureof merit would reflect that).

An additional CPR figure of merit relates to the relative amount of timespent administering chest compressions during the resuscitation event.As used herein, this figure of merit refers to a temporal CPR percentagethat represents a percentage of an event time interval (e.g., the totalevent time) during which chest compressions were administered to thepatient. In this regard, CPR assessment process 300 may determine thetemporal CPR percentage for the given event (task 324). In a practicalembodiment, CPR merit algorithm 208 can determine the temporal CPRpercentage by identifying the CPR compression cycles, marking the starttime and end time for each cycle, calculating the total amount of timespent administering chest compression cycles, and identifying the totalevent time. Thereafter, the temporal CPR percentage may be determined byexpressing the total combined chest compression time as a percentage ofthe total event time. Typically, a low temporal CPR percentage isundesirable because it indicates less time spent performing chestcompressions. In contrast, a high temporal CPR percentage is usuallydesirable because it indicates more time spent performing chestcompressions. Consequently, a low percentage will adversely affect theCPR figure of merit.

Yet another CPR figure of merit relates to the percentage of recommended“hands on time” during which the caregiver was actually administeringcompressions. For example, in an AED application, the data from thedefibrillator device may include markings indicating when voice promptswere given. The AEDs instruct the rescuer not to touch the patientduring some intervals, e.g., intervals during which the AED is analyzingthe ECG or delivering a defibrillation shock. Thus, there may be periodsof time during the resuscitation event when the rescuer should not beadministering compressions. In this regard, it is possible in post-eventreview to know exactly how much of the time the AED was “asking for” CPRto be delivered (referred to in this context as “hands on time”). Thisfigure of merit could be used to grade the compressions administeredduring the recommended hands on time.

The system may also generate one or more figures of merit related toventilations administered to the patient. For ventilation, one importantaspect is to ensure that ventilations are not provided at too high arate, because excessive ventilation rates can adversely affect thehemodynamics of CPR (for example, it is generally accepted that a rateabove approximately 20 ventilations per minute is undesirable). In otherwords, it is generally thought to be a good idea to deliver somebreaths, but important not to overdo the ventilations. Accordingly, asuitable figure of merit is responsive to a ventilation rate based uponthe number of ventilations administered to the patient during a givenevent time interval, where calculated ventilation rates that fall aboveor below a target rate adversely affect the figure of merit.

CPR assessment process 300 may generate a report (or any number ofreports) containing one or more CPR figures of merit as described above(task 326). The report may be rendered on display element 212, printed,generated in an audible format, or transmitted via facsimile or email.Of course, in a network environment, the report may be rendered on ortransmitted to any number of computing devices that are in communicationwith the remote computing device responsible for the actual processingand analysis. A simple, quantitative report that indicates theproportion or percentage of defibrillator use time occupied by chestcompressions can be useful for a number of practical reasons, including,without limitation: emergency medical services recordkeeping; caregivertraining; development of new resuscitation protocols; controlling forcertain parameters in clinical research reports or evaluations; andlegal verification that appropriate CPR was administered to the patient.Although not shown in FIG. 4, process 300 may be performed for multiplecases and may include additional tasks associated with the collectionand processing of multiple case data, which can be utilized to generatestatistical averages and/or trending data.

One refinement of CPR assessment process 300 would be to calculate theCPR figure of merit for the portion of the event that occurs before thereturn of spontaneous circulation (rather than for the entire event).This would appropriately avoid “penalizing” the figure of merit when thecaregiver has properly stopped CPR once a pulse returns. The assessmentof when a pulse or spontaneous circulation returns could be made andmanually entered by a reviewer, making use of audio recordings from thescene, from separate records of the time course of the resuscitation, orthe like. Alternatively, the assessment of spontaneous circulation couldbe determined automatically from a system that has a pulse detectioncapability, using technology designed to detect a pulse based on any ofseveral candidate physiologic measurements.

The results obtained by CPR assessment process 300 may be useful incombination with the results obtained from other algorithms such asalgorithms that analyze characteristics of the ventricular fibrillationsignal to estimate the state or viability of the patient's heart. Forexample, trend information about the characteristics of the ventricularfibrillation signal in combination with information about CPRperformance over some time interval during a resuscitation event mightprovide insight into the effectiveness of the CPR provided to thepatient, or the duration or conditions of the cardiac arrest.

The functionality of computing device 200 may also be incorporated intodefibrillator device 100, thus allowing real-time or approximatelyreal-time analysis and assessment of CPR. Results of the analysis couldbe displayed, printed, or generated in audible form by defibrillatordevice 100. Results of the analysis performed in real-time orapproximately real-time could also be used to have defibrillator device100 provide feedback to a caregiver who is in the process of providingCPR, in the form of visual or aural prompts which provide CPRinformation, guidance, or encouragement to the caregiver. For example,if the analysis shows that compressions are not being given at anappropriate frequency, aural voiced prompts could instruct the caregiverto speed up or to slow down the compression rate. As another example, ifthe analysis shows that CPR is being performed in an appropriate manner,a prompt can inform the caregiver and provide encouragement to continuethe effort (e.g., “Good job; keep going”). In such an embodiment, thepatient related data need not be “post-event” data as defined herein,however, the processing of such data would be consistent with themethodology of CPR assessment process 300.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the exemplary embodiment or exemplary embodiments. Itshould be understood that various changes can be made in the functionand arrangement of elements without departing from the scope of theinvention as set forth in the appended claims and the legal equivalentsthereof.

1. A method for assessing cardio-pulmonary resuscitation (“CPR”)performed during resuscitation therapy, said method comprising:receiving post-event data for a patient, said post-event datarepresenting at least one patient signal electronically captured duringa resuscitation event; analyzing characteristics of said post-event datato identify periods during which chest compressions were administered tosaid patient; deriving a CPR figure of merit from said post-event data,said CPR figure of merit being indicative of temporal characteristics ofCPR administered to said patient, relative to said resuscitation event;and obtaining an event time interval for said resuscitation event,wherein said resuscitation event includes at least one interval of chestcompression delivery and at least one interval of defibrillation therapydelivery, and wherein said CPR figure of merit comprises a temporal CPRpercentage representing a percentage of said event time interval duringwhich chest compressions were administered to said patient.
 2. A methodaccording to claim 1, further comprising analyzing characteristics ofsaid post-event data to identify times during said resuscitation eventwhen defibrillation pulses were administered to said patient, whereinsaid CPR figure of merit comprises a pre-defibrillation pause indicatorthat represents a period between a defibrillation pulse and a finalchest compression administered to said patient prior to saiddefibrillation pulse.
 3. A method according to claim 1, furthercomprising analyzing characteristics of said post-event data to identifytimes during said resuscitation event when defibrillation pulses wereadministered to said patient, wherein said CPR figure of merit comprisesa post-defibrillation pause indicator that represents a period between adefibrillation pulse and an initial chest compression administered tosaid patient subsequent to said defibrillation pulse.
 4. A methodaccording to claim 1, further comprising analyzing characteristics ofsaid post-event data to identify times during said resuscitation eventwhen individual chest compressions were administered to said patientduring a CPR cycle, wherein said CPR figure of merit comprises acompression frequency indicator that represents a period between saidindividual chest compressions.
 5. A method according to claim 1, furthercomprising analyzing characteristics of said post-event data to identifyCPR cycles during said resuscitation event, wherein said CPR figure ofmerit comprises a CPR cycle indicator that represents a period betweensaid CPR cycles.
 6. A method according to claim 1, further comprisinggenerating a report containing said CPR figure of merit.